Silicon Valley executives talk a lot about how the world has shifted to "Internet time." The idea is akin to dog years. What used to happen in seven years now happens in one. Or so the theory goes.

It's a cute idea. It's a useful one, too—if you're part of a company that's trying to get the rest of us to keep upgrading to ever-faster technology. In fact, technologies get adopted at nearly the same pace as they have for more than a century. Revolutions take decades.

Television needed about a quarter century to take off. The VCR, microwave, and telephone each required at least three decades to spread. Forty-six years passed before electricity found its way into the mainstream. The airplane and the automobile both sputtered along for more than 50 years. The burst of fax usage that speeded information exchange starting 20 years ago actually began 120 years earlier, when the fax was patented.

Looking at more topical examples, the Internet was set up in the 1960s but didn't become a disruptive force in business for almost 30 years. Smart cards, which may well end up being revolutionary, have been around for decades without truly catching the public imagination. Remember when John Sculley, then the chief executive officer of Apple Computer, proclaimed in the early 1990s that his Newton personal digital assistant would usher in a $1 trillion market by the year 2000? Devices like the Palm Pilot are, in fact, just now becoming important, and Mr. Sculley's prediction will be off by more than a factor of 1,000.

As Mr. Sculley's prediction shows, the real problem facing executives isn't the speed of technological change. It's the uncertainty of it.

For every fax revolution, there's a videophone, which AT&T unveiled to great applause in 1964 but which has yet to go mainstream. For every Internet, there are dozens of computer technologies, such as optical memory storage, that never quite live up to their early promise.

Even when an idea catches hold, it's usually not clear which version will win. Early on, for instance, it seemed that cars would be powered by electricity. Henry Ford's wife drove an electric car for years.

And even if you guess correctly which technologies will prevail, you'll have a hard time figuring out how the technology will be used. When the Defense Department set up the Internet, the idea was to have a communications network that could withstand a nuclear attack. Alexander Graham Bell thought the telephone would be used to broadcast classical music. Western Union didn't think people would use the telephone to exchange messages; it thought the telegraph worked just fine for this purpose. Guglielmo Marconi, the inventor of the radio, hadn't considered it for broadcast. Television was expected to replace radio completely.

Finally, even if you figure out how a new technology will be used, you almost certainly won't guess all its secondary effects. Who could have know that the car, a simple transportation device, would change the landscape by allowing for suburbs?

It's true that once a technology like the TV or the Internet reaches critical mass, its influence explodes. Change happens fast and occurs everywhere at once.

But you can actually see transforming technologies coming from miles away. You just have to aggressively sift through potentially important technologies to separate the winners from the videophones. Then you have to work hard so your business can adapt on the fly as the unpredictable effects of a technological revolution become apparent.